Lithium chloride does not inhibit the proliferation of L6 myoblasts by decreasing intracellular free inositol.
We conducted a series of experiments to determine whether lithium chloride (LiCl) inhibited the proliferation of L6 myoblasts by reducing the availability of intracellular free inositol. After the myoblasts were plated in DMEM + 10% fetal bovine serum (FBS) for 24 h, medium was replaced with DMEM + 10% FBS containing 0 (control), 5, 10, or 20 mM LiCl. Cell number, protein content, and [3H]thymidine incorporation into DNA were determined at 24-h intervals. Control cells exhibited a 3.8-fold increase in cell number by 96 h in culture. Although 5 mM LiCl did not affect the rate or extent of proliferation, 10 and 20 mM LiCl caused 36 and 86% decreases, respectively (P < .05), in cell number by 96 h in culture. The effects of LiCl could not be overcome by the addition of free inositol (up to 20 mM) to the medium. Lithium chloride caused 4.6- and 7.3-fold increases (P < .05) in lactate dehydrogenase activity in culture media after 96 h of exposure to 10 and 20 mM LiCl, respectively, indicating loss of viability after chronic treatment. However, the acute effects of LiCl after 24 h of treatment were reversible, as indicated by a rapid resumption of proliferation following removal of LiCl. Concentrations of 5, 10, and 20 mM LiCl caused 4.7-, 8.2-, and 9.1-fold increases (P < .05), respectively, in the accumulation of [3H]inositol within the inositol monophosphate pool. Treatment of cells with 10 and 20 mM LiCl also increased (P < .05) label recovered as inositol bisphosphate. Rather than depress phosphoinositide synthesis, the addition of 10 and 20 mM LiCl dose-dependently increased (P < . 05) the incorporation of [3H]inositol into phosphatidylinositol and phosphatidylinositol-4-phosphate. These results indicate that LiCl does not decrease proliferation of L6 myoblasts via a depletion in the intracellular free inositol pool. Instead, LiCl may block the hydrolysis of phosphatidyl inositides.
Laurenz
J C
JC
Department of Animal Science, Texas Agricultural Experiment Station, Texas A&M University, College Station 77843-2471, USA.
Smith
S B
SB
D000818:Animals; D002417:Cattle; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006868:Hydrolysis / Q000187:drug effects; D007294:Inositol / Q000032:analysis* / Q000378:metabolism; D007295:Inositol Phosphates / Q000032:analysis / Q000378:metabolism; D018021:Lithium Chloride / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D010716:Phosphatidylinositols / Q000032:analysis / Q000378:metabolism; D013234:Stem Cells / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D014316:Tritium; D007294:Inositol; D004247:DNA; D018021:Lithium Chloride; D013936:Thymidine